High energy density batteries are those that normally have available about 50 watt powers per pound. Recently a breakthrough has been uncovered for a new type of high energy density battery, described in U.S. Pat. No. 3,713,888 which is hereby incorporated by reference, and employs a metal halide electrolyte-halogen hydrate system. The use of such a system requires the handling of corrosive material such as chlorine, and aqueous solutions of chlorine as well as the metal halide electrolyte. Such a system is amenable to the use of bipolar electrodes such as those described in U.S. Pat. Nos. 3,813,301 and 3,909,298.
The bipolar electrodes of the aforementioned patents are those in which one face of two separate electrodes are joined together so as to form the desired bipolar electrode structure. A number of cells using the bipolar electrodes can be joined together in series to form cell banks and these can be further joined in series to increase the voltages developed, in parallel to increase the current capacity, or in mixed seriesparallel to accomplish both objectives. However, in such cell banks, the intercell distances are small, for example, four cells per 2.54 cm, which accentuates parasitic and/or dendritic effects.
It has been discovered that the problem associated heretofore with the small intercell distances can be greatly relieved by using a new bipolar electrode structure with electrical conduction across the width of the electrodes rather than through their thicknesses, a plurality of such electrode structures having their electrodes interdigitated so as to form the cell bank. It has been found that the use of this structure can increase the effective intercell distance from around 0.75 cm to about 6.35 cm or more while the actual distance between opposing electrode faces is about 0.2 cm.
Accordingly, it is the object of this invention to provide a new bipolar electrode element, and cell banks or electrode stack comprised of such elements in which the effective intercell distance is much greater than the actual interelectrode distance thereby deaccentuating the parasitic and/or dendritic effects associated with the electrochemical battery.